Apparatus and method for transmitting data in a tire condition sensing system

ABSTRACT

A tire condition sensing apparatus ( 14 ) includes a tire condition sensor ( 78, 84, 88 ) for sensing a tire condition and providing a sensor signal indicative thereof. A transmitter ( 44 ) transmits a data message having a plurality of data locations for accommodating data. A controller ( 72 ) is electrically connected with the tire condition sensor ( 78, 84, 88 ) and the transmitter ( 44 ). The controller ( 72 ) controls the transmitter ( 44 ) to transmit tire condition data in selected data locations of the data message based on a parameter associated with the apparatus ( 14 ), such as an identification code of the apparatus ( 14 ).

TECHNICAL FIELD

The present invention relates to a tire condition sensing apparatus and,more particularly, to an apparatus and method for transmitting data in atire condition sensing system.

BACKGROUND OF THE INVENTION

Numerous tire pressure monitoring systems have been developed in orderto detect when the air pressure within a tire drops below a thresholdpressure value. A system typically includes a pressure switch, aninternal power source, and a communications link that provides the tirepressure information from a location at each vehicle tire to a centralreceiver, which may be mounted on the vehicle dashboard. Thecommunications link may be a wired or wireless link.

There has been an increasing need for tire pressure monitoring systemsdue to the use of “run flat” tires in vehicles. The “run flat” tiresenable a driver to travel an extended distance after the loss of airpressure within a vehicle tire.

As more vehicles are equipped with tire pressure sensing systems, stepsmust be taken to reduce the likelihood of overlapping signals from tirepressure sensing modules. Examples of tire pressure monitoring systemsare disclosed in U.S. Pat. No. 4,316,176, U.S. Pat. No. 5,573,610, U.S.Pat. No. 5,600,301, U.S. Pat. No. 5,602,524, U.S. Pat. No. 5,612,671 andU.S. Pat. No. 5,656,993.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a tire condition sensingapparatus that includes a tire condition sensor for sensing a tirecondition. A transmitter transmits a data message having a plurality ofdata locations for accommodating data. A controller is electricallyconnected with the tire condition sensor and the transmitter. Thecontroller controls the transmitter to transmit data in selected datalocations of the data message based on an identification code of theapparatus.

Another aspect of the present invention provides a tire conditionsensing system that includes a plurality of tire condition transmittermodules. Each of the modules has a unique identification code andincludes a tire condition sensor for sensing a condition of anassociated vehicle tire. Each module also includes a transmitter which,when activated, transmits a data message having a plurality of datalocations for accommodating data. Each module also includes a controllerelectrically connected with the tire condition sensor and thetransmitter of the corresponding module. The controller controls theassociated transmitter to transmit tire condition data in data locationsof the data message selected based on the unique identification code ofthe corresponding module.

Still another aspect of the present invention provides a tire conditionsensing apparatus that includes a tire condition sensor for sensing atire condition. A transmitter transmits a data message having aplurality of data locations for accommodating data. A controller iselectrically connected with the tire condition sensor and thetransmitter. The controller controls the transmitter to transmit tirecondition data in selected data locations of the data message based on aparameter associated with the apparatus.

Yet another aspect of the present invention provides a method oftransmitting a data message from a tire condition module having anidentification code. The method includes the steps of sensing acondition of a tire and determining random data locations of a datamessage based on the identification code of the tire condition module. Adata message is transmitted, in which tire condition data indicative ofthe sensed tire condition is provided in the determined random datalocation of the data message.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the invention willbecome more apparent to one skilled in the art upon consideration of thefollowing description and the accompanying drawings in which:

FIG. 1 is a schematic block diagram of a tire condition monitoringsystem in accordance with the present invention;

FIG. 2 is a block diagram of a sensor module of the system of FIG. 1 inaccordance with the present invention;

FIG. 3 is a representation of a data message transmitted from the sensormodule of FIG. 2;

FIG. 4 is a more detailed representation of part of the data message ofFIG. 3;

FIG. 5 is an example of a random number generator for use in the sensormodule of FIG. 2; and

FIG. 6 is a timing diagram for transmission of data messages from thesensor module of FIG. 2.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

FIG. 1 schematically illustrates a vehicle 10 equipped with a tirecondition monitoring system 12 in accordance with the present invention.The system 12 includes a plurality of tire condition sensor modules 14,16, and 18 for sensing one or more tire conditions of associated vehicletires 20, 22, and 24, respectively. While for purposes of brevity threemodules 14, 16, and 18 are illustrated, there typically is one moduleassociated with each vehicle tire, including any spare tire(s) of thevehicle 10.

Each module 14, 16, 18 includes a respective internal power supply 26,28, 30 that supplies electrical energy to various circuit components ofeach associated module. In particular, each power supply 26, 28, 30 iselectrically connected to a motion detector 32, 34, 36, respectively.Each power supply 26, 28, 30 also is electrically connected with acontroller, such as an application specific integrated circuit (ASIC)38, 40, 42, and to an RF transmitter 44, 46, 48, respectively. Eachmotion detector 32, 34, 36 provides a motion signal to the associatedASIC 38, 40, 42 having an electrical characteristic or state thatindicates movement of the associated vehicle tire 20, 22, 24. Each ASIC38, 40, 42 has a plurality of operating modes responsive to the motionsignal from its associated motion detector 32, 34, 36. Each ASIC 38, 40,42, in turn, controls the operation of each module 14, 16, 18 accordingto the its current operating mode.

As described in greater detail below, each ASIC 38, 40, 42 includes oneor more sensors operative to sense one or more conditions of eachassociated vehicle tire 20, 22, 24 and/or operating parameters of theassociated module itself. The sensors provide sensor signals indicativeof the condition sensed thereby. The associated ASIC 38, 40, 42processes the sensor signals to determine desired tire condition dataand/or diagnostic information. Each ASIC 38, 40, 42 provides tirecondition data and/or diagnostic information to its correspondingtransmitter 44, 46, 48. Each transmitter 44, 46, 48, under the controlof its respective ASIC 38, 40, 42, provides an encoded data messagesignal to an associated antenna 50, 52 and 54 indicative of the datareceived from the ASIC. The antenna 50, 52, 54 transmits or broadcaststhe data message as an RF signal through free space, indicatedrespectively at 51, 53, 55. The data message may include an indicationof tire condition, diagnostic information for the associated module, anidentification (ID) code of the module, a tire ID code indicating thelocation of the module relative to the vehicle, etc.

The RF signals 51, 53, and 55 from the modules 14, 16, and 18 arereceived at an antenna 60 of the receiver module 62. The receivedsignals are decoded by appropriate circuitry of the module 62 andprovided to a controller 64. The controller 64 may include the circuitrythat decodes or demodulates the signals. Alternatively, the decodercircuitry may be external to the controller 64 and connected between theantenna 60 and the controller.

Preferably, the controller 64 is a microcontroller or microcomputerconfigured for receiving the tire condition data signals, decoding andprocessing the received signals, and providing an indication of thereceived tire condition information. For example, the controller 64 iselectrically connected to a speaker 66 for, when appropriate, providingan audible indication, e.g., a warning signal, based on the informationcontained in the data messages. Alternatively or in addition to thespeaker 66, the controller 64 is connected to a display 68 that providesa visual indication of the received tire condition and diagnosticinformation. The display 68, for example, may be an LED or LCD displayof known configuration for displaying detailed tire conditioninformation for each vehicle tire as sensed by the tire condition sensormodules 14, 16, and 18.

The controller 64, the associated display 68, and speaker 66 are poweredby a power supply 70. The power supply may be a vehicle battery, such aswhen the receiver module 62 is mounted within the vehicle 10. Thereceiver module 62 alternatively might be powered by an internal powersupply. It is also contemplated that the receiver module 62 may be ahand-held, portable device or fob that a vehicle occupant or otherindividual may carry to obtain an audible and/or visual indication ofthe tire condition and/or diagnostic information.

While, in accordance with one embodiment of the present invention, thecommunications link between the modules 14, 16, and 18 and the receiver62 has been described as being an RF link, other wireless communicationlinks could be used in accordance with the present invention.

FIG. 2 illustrates the tire condition sensor module 14 of FIG. 1 inaccordance with an exemplary embodiment of the present invention.Identical reference numbers refer to parts of the module 14 previouslyidentified with respect to FIG. 1. The sensor module 14 may beintegrated in a single package, operating as a stand alone unit for usewith the associated vehicle tire (e.g., 20 of FIG. 1).

The sensor module 14 includes sensor components which are operative tosense various conditions of the vehicle tire and/or to obtain diagnosticinformation of the module 14. In accordance with an exemplary embodimentof the present invention, the tire conditions include tire pressure andtemperature and the diagnostic information includes battery voltage. Itis also contemplated that other parameters of the tire and/or of themodule also may be monitored in accordance with the present invention.The transmitter 44 of the module 14 broadcasts a data message signalindicative of the sensed parameters, such as in a serial data format,for receipt by the central receiver (e.g., 62 of FIG. 1).

As stated above, the motion detector 32 detects movement of theassociated vehicle tire (e.g., 20 of FIG. 1), such as in response torotation or vibration thereof. Specifically, the motion detector 32 isconnected to a controller 72 of the ASIC 38 via connection 74. Themotion detector 32 provides a signal to the controller 72 in response tothe detected movement.

For example, the motion detector 32 is in the form of a normally opencentrifugal switch that closes upon the associated vehicle tire 20rotating at a predetermined rate. For example, the centrifugal switchcloses when the associated tire rotates at a rate corresponding to avehicle speed of about 10 mph or greater. When the centrifugal switch isclosed, it provides a motion signal to the controller 72, such as alogic HIGH signal at a predetermined voltage. The logic HIGH motionsignal indicates that the associated vehicle tire (e.g., 20 of FIG. 1)is rotating at a rate corresponding to at least the predeterminedvehicle speed. On the other hand, when the centrifugal switch is open,such as for vehicle speeds less than about 10 mph, a logic LOW motionsignal of a predetermined voltage, e.g. zero volts, is provided to thecontroller 72. This indicates either the absence of vehicle movement ormovement at a speed less than the predetermined vehicle speed.

The controller 72, for example, may be a microcontroller, amicroprocessor, a state machine, discrete components, another ASIC orany combination thereof. The controller 72 controls operation of themodule 14. The function of the controller 72 could be implemented ashardware and/or software.

The controller 72 sets an operating mode or state of the module 14 inresponse to the motion signal received over 74 as well as in response toother criteria. The controller 72 tracks the state of various flagconditions that vary based on monitored parameters, such as pressure,temperature, battery voltage and motion of the associated vehicle tire.The controller 72 controls transitions between operating modes accordingto the particular value of each of the flag conditions. The controller72 also controls the timing of tire condition measurements and thetiming transmission of data messages.

The controller 72 has an output 75 connected to a control switch 76 forcontrolling activation of other components of the sensor module 14. Inparticular, the control switch 76 has an input electrically connected tothe power supply 26, such as through an appropriate filter and/orvoltage regulator (not shown). The switch 76 also has an outputconnected to various circuit components located within the ASIC 38. Thecircuit components could, in accordance with the present invention, belocated external to the ASIC 38.

While, for purposes of brevity, a single switch 76 is illustrated asconnecting components to the power supply 26, the controller 72alternatively could control each of the components through separateswitches or an appropriate switching matrix. The switches may be locatedexternal to the controller 72, such as shown with switch 76 in FIG. 2.Alternatively, one or more switches may be integrated as part of thecontroller 72 so as to provide desired electrical energy to selectedcomponents.

A pressure sensor 78 that is operative to sense tire pressure of theassociated vehicle tire (e.g., 20 of FIG. 1) is connected to the switch76. The pressure sensor 78 provides a tire pressure signal 80 to aninput of a multiplexer circuit 82 indicative of the sensed tirepressure. In particular, the pressure sensor 78 provides the tirepressure signal 80 when activated by the control switch 76. The pressuresensor 78, for example, may be an analog pressure sensing device, suchas a Wheatstone bridge, that provides a signal having an electricalcharacteristic (e.g., a voltage differential) indicating an absoluterelative pressure detected by the sensor 78. The pressure sensor 78 iscapable of sensing pressure within a range, for example, from about 50kPa to about 640 kPa over a wide temperature range.

A temperature sensor 84 also is connected to the switch 76 and to aninput of the multiplexer circuit 82. The temperature sensor 84 providesa signal 86 to the multiplexer circuit 82 having an electricalcharacteristic indicative of the sensed temperature of the associatedvehicle tire. The controller 72 controls operation of the temperaturesensor 84 through activation of the control switch 76.

A battery voltage sensor 88 is electrically connected between theinternal power supply 26 and an input of the multiplexer circuit 82. Thevoltage sensor 88 samples the voltage of the power supply 26 uponactivation of the control switch 76 by the controller 72. The voltagesensor 88 provides a battery voltage signal 90 to the multiplexercircuit 82 having an electrical characteristic indicative of the sensedvoltage. The value of the battery voltage signal 90 after each broadcastprovides a good indication of the electrical energy available in thepower supply 26.

The multiplexer circuit 82 thus receives parallel input signals 80, 86and 90 from the respective sensing components 78, 84 and 88. Themultiplexer circuit 82, in turn, provides a multiplexed serial outputsignal 92, indicative of the sensed parameters from each of the sensors78, 84 and 88. The controller 72 also could be connected to themultiplexer circuit 82 to further control the multiplexing functionthereof. The multiplexed data signal 92 is provided to ananalog-to-digital converter (A/D) 94 which provides a digitized outputsignal 96 to a calibration function 98. Alternatively, the signals fromthe sensors 78, 84, and 88 could be digitized prior to being provided tothe multiplexer circuit 82.

The calibration function 98, which may be hardware and/or software, isconfigured to de-multiplex the digitized data signal 96 received fromADC 94 and calibrate the data into a readable format for the controller72. For example, the calibration function 98 may include a plurality ofpressure curves, temperature curves and/or look-up tables from whichcalibrated temperature and pressure values are determined based on theinformation contained in the digitized data signal 96. The look-up tableand curves are derived from empirical data over a wide range oftemperature and pressure for the particular pressure and temperaturesensors 78 and 84 being used. The calibration function 98 also includesa look-up table for converting the digitized voltage signal into acalibrated voltage value in a useable format.

The calibration block 98 provides a calibrated output signal 100 toanother input of the controller 72. The signal 100 has a characteristicor value indicative of each of the sensed parameters, e.g., pressure,temperature, and battery voltage. The controller 72 receives thecalibrated data signal 100 and stores at least some of the received datain appropriate memory (not shown).

The controller 72 also is programmed with a unique identification (ID)code for the transmitter 44 of the module 14 and, optionally, a tire IDcode. The transmitter ID code is set at the manufacturer. The tire IDcode may be set at the factory or by a technician who installs themodule. The tire ID code is set to indicate the tire location of themodule 14 relative to the vehicle.

The controller 72 is electrically connected with the transmitter 44 forcontrolling transmissions of the data message through the associatedantenna 50. The broadcast of the data message signal occurs at selectedtimes based on the particular operating mode of the ASIC 38. Thecontroller 72 determines the operating mode of the ASIC 38 in responseto both the motion signal received over connection 74 and in response tothe sensed parameters indicated by the calibrated output signal 100.

The controller 72 has a first operating mode, hereinafter referred to asthe normal operating mode, in response to the motion signal indicatingat least a predetermined rate of rotation of the associated vehicletire, i.e., the centrifugal switch is closed. In the normal operatingmode, for example, the controller 72 controls the switch 76 to effectperiodic activation of the tire condition sensors 78, 84 and 88 as wellas the other circuit components 82, 94 and 98 of the ASIC 38.Accordingly, sensors 78, 84 and 88 periodically sense the tire conditionof the associated vehicle tire at a predetermined rate, such as aboutonce every four to ten seconds. Also, in the normal operating mode, thecontroller 72 controls the RF transmitter 44 to broadcast the datamessage signal. The broadcast of each data message signal occursintermittently at random time intervals within a variable time window,such as ranging from about three to about five minutes. This helps toreduce the overlap and interference of data messages from other sensormodules (e.g., 16, 18 of FIG. 1).

When the centrifugal switch 32 is opened, thereby indicating rotation ofthe vehicle tire at a rate corresponding to less than a predeterminedvehicle speed, the controller 72 controls the sensor module 14 tooperate in a second, different operating mode. The second operating modeis referred to as a sleep mode.

In the sleep mode, the controller 72 controls the switch 76 to activateeach of the tire condition sensors 78, 84, and 88 so as to sense theirrespective parameters at a periodic rate that is substantially slowerthan the rate at which corresponding tire conditions are sensed when inthe normal operating mode. In the sleep mode, for example, the sensors78, 84, and 88 are controlled to sense the tire conditions about every15 minutes.

However, rather than intermittently broadcasting at random timeintervals, as in the normal operating mode, the tire condition datasignal is broadcast in the sleep mode only after one or more of thesensed tire conditions is determined to be below a predeterminedthreshold. For example, when in the sleep mode, the controller 72controls the transmitter 44 to broadcast the tire condition data signalonly after first determining that the sensed tire pressure is below apredetermined threshold, such as about 220 kPa or about 18 psi. Thebroadcasting alternatively could be based on determining that the sensedtemperature is at or above some predetermined level or that the sensedbattery voltage is below a voltage threshold.

The sleep mode helps to conserve the energy of the internal power supply26 when the vehicle is parked or otherwise not being used. The sleepmode advantageously still provides for relatively frequent measurementsof the tire condition so that upon determining the occurrence of, forexample, a low tire pressure condition, this information is provided tothe driver upon starting the vehicle as key-on-status information. Therestricted broadcasts in the sleep mode further help to reduceinterference with other RF communication links of the vehicle, such as aremote keyless entry system, that typically occur when the vehicle isstationary. Other operating modes also may be used to control thefrequency of parameter measurements as well as transmission of the datamessage signals.

Referring to FIG. 3, a data message 120 has a time interval, indicatedat 122. The data message 120 is subdivided into a plurality of dataframes, such as five, indicated as FRAME 1 through FRAME 5. The timeinterval of FRAME 1 is indicated at 124. Each frame preferably has thesame time interval. Each data frame is further divided into a pluralityof time slots 126 into which desired data may be provided. In thisexample, there are four time slots per frame, although other numbers oftime slots per frame could be used. The grouping of data that isprovided in a time slot 126 is hereinafter referred to as a data packet.The duration of a time slot is indicated at 128 and the duration of adata packet is indicated at 130.

By way of example, FIG. 4 illustrates a functional example of a datapacket 130 that extends an interval indicated at 132. Each data packet126 in a data message includes a plurality of data bits that containsselected data. In this example, starting from the left side of FIG. 4,the data packet 130 includes a start pulse followed by a preamble thatcontains synchronization information for the data packet. Next, the datapacket contains calibrated data indicative of one or more of the sensedparameters, including at least one of temperature, battery voltage, andpressure. The data packet 126 also contains data indicating the type ofcalibrated data being indicated in the data packet.

Next, the data packet 130 contains data corresponding to the tire IDcode and the transmitter ID code. For example, the tire position ID codemay comprise three bits while the transmitter ID code may comprise 19bits. Following the ID code information, the data packet 130 includesdata bits indicating the current operating mode of the transmitter. Inaddition, data bits are provided to indicate temperature status, such aswhether the sensed temperature is normal, invalid, a low temperature, ora high temperature. Error bits also may be provided for indicating a lowbattery condition or other internal errors detected by the controller atthe sensor module. A cyclic redundancy check (CRC) of the proceedingdata also is provided in the data packet 130 for error detection.

In accordance with an exemplary embodiment of the present invention,each data frame contains two data packets located in selected dataslots. A data packet is positioned in the first slot of each frame. Thesecond data packet in each frame of the data message is located in atime slot randomly selected from the three remaining slots per frame perdata message. The random location for the second data packet in a frameis determined based on a selected parameter of the module 14. Theparameter, for example, could be the transmitter ID code or a sensedtire condition, such as pressure, temperature, wheel speed, etc.

In accordance with an exemplary embodiment of the present invention, thetime slot selection for the second data packet is determined by a randomnumber generator, which may be hardware and/or software. The randomnumber generator selects a time slot in each frame of the data messagebased on a parameter associated with module 14. As mentioned above, theparameter could include the transmitter ID code, the tire position IDcode and/or a sensed tire condition (e.g., pressure, temperature, wheelspeed, etc.). In particular, the parameter is used to initialize or seedthe random number generator. The random number generator, in turn,modifies or shifts its values for each frame so as to provide a randomvalue associated with a data slot locations for each frame of the datamessage.

An example of a random number generating algorithm 200 is illustrated inFIG. 5. The algorithm 200 is a cyclic block coding scheme seeded by thetransmitter ID code and the tire position ID code. In this example, thetransmitter ID code is formed of 19 bits (ID0-ID18) and the tireposition ID code has three bits (TID0-TID2). The random numbers aregenerated through the rotation of data through linear feedback shiftregisters and by Boolean operations performed on the data being shifted.The algorithm 200 may be implemented as hardware and/or software. Whilethe example illustrated in FIG. 5 is a bitwise algorithm, larger unitsof bits could be used and may be combined with other arithmeticoperations to help generate random numbers.

Referring to FIG. 5, the algorithm 200 includes a register 202 intowhich some of the transmitter ID bits (ID0-ID14) are stored. Thealgorithm 200 also includes another register 204 into which theremaining transmitter ID bits (ID15-ID18) are stored together with thetire position ID bits (TID0-TID2). At power on, the transmitter ID bits(ID0-ID14) are latched from the register 202 into a shift register 206.This typically occurs at the manufacturing plant when the battery (e.g.,26 of FIG. 2) is connected to the module. Also at power on, the othertransmitter ID bits (ID15-ID18) along with the tire position ID bits(TID0-TID2) are latched from the register 204 into registers b0-b6 of afeedback shift register 208. Specifically, ID15 is latched into b0, ID16is latched into b1, ID17 is latched into b2, ID18 is latched into b3,TID0 is latched into b4, TID1 is latched into b5, and TID2 is latchedinto b6. In the situation when no tire position ID code is programmed, apredetermined bit value of 0 or 1 is stored in memory (e.g., TID0-TID2)of the controller, which values are latched into registers b4-b6 atpower on.

Each time the shift register 208 is clocked, the values of each registerb0-b6 is shifted in the direction of the corresponding arrows. Inaddition, the values of BIT0-BIT13 are shifted one space to the rightfor each clock pulse provided to register 206. Preferably, the registers206 and 208 are clocked simultaneously. An Exclusive OR function 212Exclusive ORs the value of BIT14 of register 206 with the value ofregister b6 each time the algorithm 200 is shifted. The value b6 also isfed as feedback into BIT0 of the shift register 206 each time theregister 200 is shifted.

The output value of the Exclusive OR function 212 is provided asfeedback to two other Exclusive OR functions 214 and 216, as well asbeing loaded into the shift register b0 at each clock pulse. The valueof shift register b1 is Exclusive ORed together with the output value ofthe Exclusive OR function 212 which is, in turn, shifted into b2.Similarly, Exclusive OR function 216 performs an Exclusive OR operationon the output value of Exclusive OR function 212 and the value ofregister b5. The output value of the Exclusive OR function 216 isprovided to register b6 at the next clock pulse.

In accordance with an exemplary embodiment of the present invention, thevalues of shift registers b5 and b6 provide a two bit random number usedto select the second slot of a given frame. Data is shifted in thealgorithm 200 at least once for each data frame so that a differentrandom value may be provided for slot selection in each frame.

By way of example, Table 1 illustrates the correlation of the randombinary values of registers b5 and b6 to the slot selection for thecurrent frame for the situation where there are four slots per frame.Other numbers of slots per frame could be used in accordance with thepresent invention. Similarly, the values of registers b0-b4 providesanother random number (e.g., a decimal value of 0-31) that is used inthe time measurement interval between transmissions of subsequent datamessages.

TABLE 1 Random Value Selected Slot 00 Slot 2 01 Slot 3 10 Slot 3 11 Slot4

Each tire transmitter module of the system (e.g., 12 of FIG. 1) includessuch a random number generating algorithm 200. Each algorithm isinitialized with a unique number, namely, the transmitter ID code and(when used) the tire position ID code. The ID code values are shiftedinto the feedback shift register over a period of shifts and then theresults are continually rotated through the feedback shift register. Inthis way, the values of the different registers b0-b6 are manipulated tocontinually generate random numbers at registers b0-b6.

The content of the data packet also may vary as a function of theoperating mode of the module. For example, in a normal mode and apressure alert mode, slot one in each frame contains pressure data. Thesecond packet in frame 3 contains temperature data, the second packet inframe 4 contains battery voltage data, and a second packet in frame 5contains other parameters, such as data indicating the value of a runflat counter. In a temperature alert mode, slot one in each framecontains pressure data while the second packet in each frame containstemperature data.

FIG. 6 illustrates an example of a timing diagram for two data messages(DATA_MESSAGE 1, DATA_MESSAGE 2) formatted according the above-describedmethod. DATA_MESSAGE 1 includes a plurality of data frames, whichincludes a data packet is located in the first time slot of each frame.A second data packet is located in the last time slot of the firstframe, and a second data packet is located in the second time slot ofthe second frame. This is based on registers 65 and 66 of FIG. 5 havinga binary value of 11 when FRAME 1 is packaged and a binary value of 00when FRAME 2 is packaged. For purposes of brevity, only one frame of theDATA_MESSAGE 2 is illustrated in which a data packet is located in thefirst time slot. A second data packet is located in the third time slotin response to the value of registers b5 and b6 providing a binary valueof either 01 or 10.

The repetition interval between data message transmissions, indicated at230, is state dependent. In order to comply with FCC regulations,however, a minimum interval of 15 seconds must be held between datamessage transmissions. In order to further help avoid collision betweentransmissions of data messages, the length of the time interval 230 israndomized. The bits b0-b4 of the feedback shift register 208 of FIG. 5provide a random number that is used to vary the length of thetransmission time interval. The time interval further may vary accordingto the particular operating mode of the module. For example, in thenormal mode the time interval 230 may be provided by (32+n)×t_(m), wheren is a random number in the range of 0 to 31 which is read fromregisters b4-b0 of the feedback register of the random number generatorand t_(m) is the measurement interval over which the sensor measurementswere taken, such as a nominal interval of 7.2 seconds.

In accordance with another aspect of the present invention, the timingof the first data transmission after activation of the motion detectoralso is based on at least some of the transmitter ID code and tireposition ID code values. By way of example, the first transmission of adata message is delayed by a binary value of (TID2-TID0, ID18-ID14)×22milliseconds. This initial delay is indicated at 232 in FIG. 6.

In view of the foregoing, the present invention provides an apparatusand method for helping avoid collision of data messages in a tirepressure sensing system. The controller of the transmitter varies thelocations of selected data packets as a function of a random numbergenerated using a parameter associated with the transmitter module, suchas the transmitter ID code and, optionally, the tire position ID code.The controller of the transmitter module also may vary the intervalbetween adjacent data messages based on the transmitter ID code and/orthe tire position ID code.

In view of the foregoing, the present invention provides a system andmethod in which desired the tire condition data is transmitted inselected data slots in each frame of each data message.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications. Suchimprovements, changes and modifications within the skill of the art areintended to be covered by the appended claims.

Having described the invention, the following is claimed:
 1. A tirecondition sensing apparatus comprising: a tire condition sensor forsensing a tire condition; a transmitter for transmitting a data messagehaving a plurality of data locations for accommodating data; and acontroller electrically connected with said tire condition sensor andsaid transmitter, said controller controlling said transmitter totransmit tire condition data in selected data locations of said datamessage based on an identification code of said apparatus.
 2. Anapparatus as set forth in claim 1 wherein said selected data locationsof said data message are randomly determined based on the identificationcode of said apparatus.
 3. An apparatus as set forth in claim 2 whereinsaid data message is a serial data message which includes a plurality offrames, each of said frames having a plurality of data locations, saidcontroller controlling said transmitter to provide tire condition datain a randomly selected data location of each frame of said data message,the location of said randomly selected data location being determinedbased on the identification code of said apparatus.
 4. An apparatus asset forth in claim 3 wherein said controller further includes means fordetermining a randomly selected data location for each frame of eachdata message transmitted by said transmitter.
 5. An apparatus as setforth in claim 4 wherein said determining means is a random numbergenerator initialized by the identification code of said apparatus, saidrandom number generator providing a signal having value indicative ofthe randomly selected data location for each frame of each data messagetransmitted by said transmitter.
 6. An apparatus as set forth in claim 3wherein said controller controls said transmitter to provide firstdesired data in a first data location of each frame of said data messageand provide other desired tire condition data in a randomly selectedsecond data location of each frame of said data message.
 7. An apparatusas set forth in claim 6 wherein said controller has a plurality ofoperating modes and the content of the other desired tire condition datafor each frame of said data message varies based on the operating modeof said controller.
 8. An apparatus as set forth in claim 2 wherein theselected data locations further vary based on the location of saidtransmitter relative to a vehicle in which said apparatus is mounted. 9.An apparatus as set forth in claim 1 further including a motion detectorelectrically connected to said controller, said motion detectorproviding a motion signal to said controller indicative of vehiclemotion, said controller activating said tire condition apparatus inresponse to the motion signal.
 10. An apparatus as set forth in claim 9wherein said controller, when activated in response to the motionsignal, controls said transmitter to delay transmission of tirecondition information a duration responsive to the identification codeof said apparatus.
 11. An apparatus as set forth in claim 10 wherein theduration of transmission delay is randomly determined based on theidentification code of said apparatus.
 12. A tire condition sensingsystem for a vehicle comprising: a plurality of tire pressuretransmitter modules, each of said plurality of modules having a uniqueidentification code and including: a tire condition sensor for sensing acondition of the associated tire; a transmitter for, when activated,transmitting a data message having a plurality of data locations foraccommodating tire condition data for the associated vehicle tire; and acontroller electrically connected with said tire condition sensor andsaid transmitter, said controller controlling said transmitter totransmit tire condition data in randomly selected data locations of saiddata message, the randomly selected data locations being determinedbased on the unique identification code of said module.
 13. A system asset forth in claim 12 wherein the data message from each of saidtransmitters is a serial data message that includes a plurality offrames, each of said frames having a plurality of data locations, eachof said controllers controlling the associated one of said transmittersto provide tire condition data in a randomly selected data location ofeach frame of the data message, said randomly selected data location ofeach frame being determined based on the identification code of theassociated one of said modules.
 14. A system as set forth in claim 13wherein each of said controllers has a plurality of operating modes andcontrols the associated one of said transmitters to provide firstdesired tire condition data in a first data location of each frame ofsaid data message and provide other desired tire condition data in arandomly selected second data location of each frame of said datamessage, the content of the other desired tire condition data for eachframe of said data message varying based on the operating mode of theassociated one of said controllers.
 15. An apparatus as set forth inclaim 13 wherein the randomly selected data locations further vary basedon a programmed location of the associated one of said transmittersrelative to a vehicle in which said apparatus is mounted.
 16. Anapparatus as set forth in claim 13 wherein each of said controllersfurther includes means for determining a randomly selected data locationtire condition data in each data message transmitted by the associatedone of said transmitters.
 17. An apparatus as set forth in claim 16wherein said determining means is a random number generator initializedwith the identification code of the associated one of said modules, saidrandom number generator providing a signal having value indicative ofthe randomly selected data location for tire condition data in each datamessage transmitted by the associated one of said transmitters.
 18. Atire condition sensing apparatus comprising: a tire condition sensor forsensing a tire condition; a transmitter for transmitting a data messagehaving a plurality of data locations for accommodating data; and acontroller electrically connected with said tire condition sensor andsaid transmitter, said controller controlling said transmitter totransmit tire condition data in selected data locations of said datamessage based on a parameter associated with said apparatus.
 19. Anapparatus as set forth in claim 18 wherein said apparatus has a uniqueidentification code, said parameter associated with said apparatus beingfunctionally related to said identification code of said apparatus. 20.An apparatus as set forth in claim 18 wherein said parameter associatedwith said apparatus is functionally related to the sensed tirecondition.
 21. An apparatus as set forth in claim 18 wherein saidcontroller further includes means for determining randomly selected datalocations in said data message based on the parameter associated withsaid apparatus, said controller controlling said transmitter to transmittire condition data in the determined randomly selected data locationsin each data message transmitted by said transmitter.
 22. An apparatusas set forth in claim 21 wherein said determining means is a randomnumber generator initialized by the parameter of said apparatus, saidrandom number generator providing a signal having value indicative ofsaid randomly selected data location in each data message transmitted bysaid transmitter.
 23. A method of transmitting a data message from atire condition module, comprising the steps of: sensing a condition of atire; determining random data locations of a data message based on anidentification code of the tire condition module; and transmitting adata message in which tire condition data indicative of the sensed tirecondition is provided in the determined random data locations of thedata message.
 24. A method as set forth in claim 23 wherein the datamessage is a serial data message which includes a plurality of frames,each of said frames having a plurality of data locations, said methodfurther including providing tire condition data in a random datalocation of each frame of the data message, the random data locationbeing determined based on the identification code of the tire conditionmodule.
 25. A method as set forth in claim 24 wherein said step ofdetermining further includes initializing a random number generatorbased on the identification code of the tire condition module, saidrandom number generator providing a signal having value indicative ofeach random data location in each transmitted data message.
 26. A methodas set forth in claim 24 wherein first desired tire condition data isprovided in a first data location of each frame of the data message andsecond desired tire condition data is provided in a randomly determinedsecond data location of each frame of the data message.
 27. A method asset forth in claim 26 wherein said step of transmitting repeats at arate according to a selected one of a plurality of operating modes, thecontent of the second desired tire condition data for each frame of saiddata message being determined based on the operating mode of saidcontroller.
 28. A method as set forth in claim 27 further including thesteps of detecting movement of the vehicle, determining the selected oneof the operating mode based on the detected movement of the vehicle, andactivating the transmitter in response to the detected movement of thevehicle.
 29. A method as set forth in claim 28 further including thestep of delaying said step of transmitting the data message a durationbased on the identification code of the tire condition module upon thetransmitter being activated.
 30. An method as set forth in claim 29wherein the duration of transmission delay is determined randomly basedon the identification code of the tire condition module.